Fix the backup API so that a backup from an empty database to a non-empty

database works.  Ticket [0bf974bdf9].  The only changes are in assert()
statements.

FossilOrigin-Name: ddb71cd9ed395804a13dc136bb7688a7627c798f

2 files changed, 14 insertions, 1 deletions

diff --git a/src/os_unix.c b/src/os_unix.c
index b31fbab21..0a866f155 100644
--- a/src/os_unix.c
+++ b/src/os_unix.c
@@ -3113,6 +3113,19 @@ static int unixTruncate(sqlite3_file *id, i64 nByte){
     ((unixFile*)id)->lastErrno = errno;
     return SQLITE_IOERR_TRUNCATE;
   }else{
+#ifndef NDEBUG
+    /* If we are doing a normal write to a database file (as opposed to
+    ** doing a hot-journal rollback or a write to some file other than a
+    ** normal database file) and we truncate the file to zero length,
+    ** that effectively updates the change counter.  This might happen
+    ** when restoring a database using the backup API from a zero-length
+    ** source.
+    */
+    if( ((unixFile*)id)->inNormalWrite && nByte==0 ){
+      ((unixFile*)id)->transCntrChng = 1;
+    }
+#endif
+
     return SQLITE_OK;
   }
 }
diff --git a/src/pager.c b/src/pager.c
index 9686eb904..1c8fd8314 100644
--- a/src/pager.c
+++ b/src/pager.c
@@ -4446,7 +4446,7 @@ static int pager_incr_changecounter(Pager *pPager, int isDirectMode){
 #endif
 
   assert( pPager->state>=PAGER_RESERVED );
-  if( !pPager->changeCountDone && ALWAYS(pPager->dbSize>0) ){
+  if( !pPager->changeCountDone && pPager->dbSize>0 ){
     PgHdr *pPgHdr;                /* Reference to page 1 */
     u32 change_counter;           /* Initial value of change-counter field */